1. Field of the Invention
The present invention relates to interference monitoring techniques and in particular to a technique which alerts a user to deteriorated communication quality caused by occurrence of interference in a radio communication system.
2. Description of the Related Art
In recent years, it has become a common practice to obtain access to the Internet from ordinary households. In order to eliminate the inconvenience and disorder of cabling from a telephone line to information devices within a home, wireless connections for Internet access have received widespread attention.
As such a wireless communication system, the followings are known: Wireless LAN (Local Area Network) conforming to IEEE802.11b standards (e.g. IEEE std 802.11b-1999, Supplement to IEEE Standard for Information technology—Telecommunications and information exchanger between systems—Local and metropolitan area networks Specific requirements—Part 11: wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer (PHY) Extension in the 2.4 GHz Band); and Wireless system called “Bluetooth™” which is defined in Specification of the Bluetooth™ System Version 1.0B. These wireless systems are used in the 2.4 GHz band.
In radio communications, quality of communication is frequently affected by the presence of other electric equipment generating radio waves at frequencies in the same band. In order to avoid the effect of interference from such other electric equipment, several techniques have been proposed. In Japanese Patent Application Unexamined Publication No. 07-143090, a received electric field strength is compared with a reference level to produce a level signal and, when the period of high level is longer than the time width of a time slot, an alarm is generated. In Japanese Patent Application Unexamined Publication No. 2000-022712, a channel use state of its own radio communication system is measured for each channel and a channel use state (for example, interference power) of other radio communication system is also measured. When interference is detected, a channel to be used for its own radio communication system is automatically changed.
The above prior arts are designed to decrease the effect of interference when the radio communication system is in operation. In an ordinary household or the like, however, it is preferable to previously check whether interference occurs, and the result is used to design a radio communication system within the household to provide no interference.
In the case where a radio communication system has no interference avoiding technique such as the above prior art implemented therein, it is difficult to handle deteriorated performance problems cause by occurrence of interference. As a result, an expected communication performance cannot be obtained.
In Japanese Patent Application Unexamined Publication No. 05-136747, a directional coupler is connected between a radio transmitted an antenna to detect an unexpected reflected wave, which results in preventing damage to the transmitter and the antenna. In this publication, it is suggested that such technique can be also applied to interference detection. However this conventional technique can be applied to a radio transmitter. Accordingly, possible interference cannot be estimated until such a radio transmitter is possessed.